Differential stable isotope labeling of peptides for quantitation and de novo sequence derivation.

We have demonstrated the use of per-methyl esterification of peptides for relative quantification of proteins between two mixtures of proteins and automated de novo sequence derivation on the same dataset. Protein mixtures for comparison were digested to peptides and resultant peptides methylated using either d0- or d3-methanol. Methyl esterification of peptides converted carboxylic acids, such as are present on the side chains of aspartic and glutamic acid as well as the carboxyl terminus, to their corresponding methyl esters. The separate d0- and d3-methylated peptide mixtures were combined and the mixture subjected to microcapillary high performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Parent proteins of methylated peptides were identified by correlative database searching of peptide tandem mass spectra. Ratios of proteins in the two original mixtures could be calculated by normalization of the area under the curve for identical charge states of d0- to d3-methylated peptides. An algorithm was developed that derived, without intervention, peptide sequence de novo by comparison of tandem mass spectra of d0- and d3-peptide methyl esters.     

The selectope for cooperative games

The selectope of a cooperative transferable utility game is the convex hull of the payoff vectors obtained by assigning the Harsanyi dividends of the coalitions to members determined by so-called selectors. The selectope is studied from a set-theoretic point of view, as superset of the core and of the Weber set; and from a value-theoretic point of view, as containing weighted Shapley values, random order values, and sharing values. Received May 1997/Revised version September 1999     

Multi-Dimensional Homoclinic Jumping and the Discretized NLS Equation

We consider a class of dynamical systems that arise frequently in multi-mode truncations and discretizations of partial differential equations, including the perturbed NLS. We develop a general method to detect the existence of multi-pulse solutions that are doubly asymptotic to an invariant manifold with two different time scales. We use our method together with some recent results of Li and McLaughlin to show the existence of several families of multi-pulse orbits for the Ablowitz-Ladik discretization of the perturbed NLS. These orbits include N-pulse heteroclinic orbits and N-pulse Šilnikov-type orbits for arbitrarily large N. Received: 1 September 1995 \ Accepted: 23 May 1997     

Electronic properties of hydrogen-related complexes in pure semiconductors

Hydrogen has been shown to activate the neutral impurities carbon, silicon and oxygen in ultra-pure germanium and form shallow level complexes. The double acceptors beryllium and zinc in silicon and germanium, as well as the triple acceptor copper in germanium, can be partially passivated, leading to single hole acceptors. The study of the electronic level spectrum of the single carrier bound to these centers at low temperatures has provided much information on symmetry and composition. Most centers reveal a symmetry axis along [1 1 1] and are static. In some cases hydrogen has been found to tunnel between equivalent real space positions. hoto hermal onization pectroscopy (PTIS) has been the most important tool for the study of the optical transitions of the hole (electron) in these hydrogen containing complexes. This photoconductivity technique combines high sensitivity with high resolution and permits the study of shallow acceptors or donors present at concentrations as low as 10⁸ cm^-3. Even lower limits may be attained under favorable circumstances.     

Effects of electronically neutral impurities on muonium in germanium

Low-temperature measurements of muonium parameters in various germanium crystals have been performed. We have measured crystals with different levels of neutral impurities, with and without dislocations, and with different annealing histories. The most striking result is the apparent trapping of Mu by silicon impurities in germanium.     

Immobilization of binding proteins on nonporous supports

Four different nonporous particulate materials, nylon, polystyrene, soda-lime silicate glass, and fused silica glass, have been evaluated for their appropriateness as immobilization supports for immunoglobulins. A method of protein quantitation that is usually applied to solutions, the bicinchoninic acid (BCA) assay, was used successfully to directly measure ng amounts of protein immobilized on the supports. Two proteins, a monoclonal antibody to theophylline and the biotin binding protein avidin, were studied. Radioactive theophylline and radioactive biotin were used to measure the activity of the immobilized protein. Ligand binding capacity per mm2 of support was measured as a function of amount of protein immobilized. By measuring both the amount of protein immobilized and its ligand binding capacity, we have determined that antitheophylline antibody adsorbed on polystyrene balls loses almost 90% of its binding activity after 65 h, although little protein is lost from the balls over this time. Avidin retains nearly full activity for biotin on polystyrene. The binding activity of biotinyl-antibody conjugate immobilized on avidin-adsorbed polystyrene is stable, even when stored for over 22 wk. Antibody covalently immobilized on soda-lime silicate glass beads retains its binding activity over long-term storage, although only 0.1 mol of 3H-theophylline bind per mol of immobilized antibody. Using fused silica glass particles as the solid support, the same antibody binds approx 0.6 mol of ligand per mol of immobilized antibody protein. The structural "softness" of the immunoglobulin requires that interaction with the surface be prevented in order to maintain activity.     

The exciting oxidation of CO on Pt

An uncollimated molecular beam (free jet) of CO and O₂ molecules incident on a polycrystalline Pt surface at 775 K in vacuo produces vibrationally hot CO₂ molecules at a density sufficient for infrared emission spectrometry. Analysis of spectra at a resolution of 0.1 cm^?1 clearly shows that nascent product molecules have much more internal excitation than would be the case for equilibrium at the surface temperature.